Based on how publishers are treating GeForce, there will never be a netflix of gaming. They would rather have their own services than allow that to happen. PSNow would mainly be for Sony 1st party IPs as licensing expires and other services kick off. However their IPs do hold enough weight to give the service value.
The thing is, it is still most profitable to maximize individual sales outside of the service. They are just doing what works right now. Some newer games do get added for limited time to help boost the service, but it is not their main business goal like it is for MS.
If streaming does every take off however (which is questionable due to publishers themselves, thank god), the infrastructure is there and they can easily adapt. There is just no reason to put a major focus on it yet. I do feel that as the PS5 drops, you will see a lot more 1st party PS4 games pop up. It may not be their primary business goal, but they will do what they can to keep it alive and develop it for if they ever need to lean on it.